The discovery of a vast number of disease biomarkers and the establishment of miniaturized fluidic systems have opened up new avenues to devise methods and systems for the prediction, diagnosis and monitoring of treatment of diseases in a point-of-care setting. Point-of-care testing is particularly desirable because it rapidly delivers results to patients and medical practitioners and enables faster consultation between patients and health care providers. Early diagnosis allows a practitioner to begin treatment sooner and thus avoiding unattended deterioration of a patient's condition. Frequent monitoring of appropriate parameters such as biomarker levels and concentrations of therapeutic agents enables recognition of the effectiveness of drug therapy or early awareness that the patient is being harmed by the therapy. Examples of point-of-care analyses include tests for glucose, prothrombin time, drugs of abuse, serum cholesterol, pregnancy, and ovulation.
Fluidic devices can utilize a number of different assays to detect an analyte of interest in a sample of bodily fluid from a subject. In ELISA assays (a preferred technique for clinical assays especially in a point-of care context, if assay reagents such as enzyme-antibody conjugates and enzyme substrates remain on-board the fluidic device after the assay is performed, reagents unbound to the assay capture surface or excess reagents, if collected in the same fluidic device, can react with one another and create a signal that can interfere with the signal of interest produced by the assay. This is especially the case in luminogenic assays in which the assay reagents generate light, in contrast to assays that measure, for example, absorbance or fluorescence. Many luminogenic assays use an enzyme to generate luminescence thus improving assay sensitivity by amplification of the measured species. Moreover, in assay systems that contain all assay components, including waste washes in a small housing the potential for glowing luminogenic waste materials is further enhanced. In such assay formats, the excess or unbound enzyme-labeled reagent may react with enzyme substrate, thus creating undesired interfering signals.
Some fluidic device features may mitigate the problem of an interfering signal to a certain degree. For example, the body of the fluidic device can be opaque, optically isolating the undesired glow, or the detection system can be configured to reject light which does not originate from reaction sites within the fluidic device. These mitigating features, however, may not sufficiently eliminate the interference as light can still travel through transparent elements of the fluidic device and interfere with the signal of interest. This is especially the case in assays requiring high sensitivity where the ratio between the signal generated from the assay may represent only a small fraction, e.g., less than 1 part in 10,000, of the total signal generating reagent.
Thus, there remains a considerable need for improved fluidic devices, especially point-of-care devices, designed to minimize interfering optical signals.